Many methods have been developed for obtaining the three dimensional location of surface points of an object, for a host of applications including, inter alia, the intraoral cavity. Techniques for direct non-contact optical measurement, in particular for direct optical measurement of teeth and the subsequent automatic manufacture of dentures, are known. The term “direct optical measurement” signifies surveying of teeth in the oral cavity of a patient. This facilitates the obtainment of digital constructional data necessary for the computer-assisted design (CAD) or computer-assisted manufacture (CAM) of tooth replacements without having to make any cast impressions of the teeth. Such systems typically include an optical probe coupled to an optical pick-up or receiver such as charge coupled device (CCD) and a processor implementing a suitable image processing technique to design and fabricate virtually the desired product. Such methods include, for example, confocal imaging techniques as described in WO 00/08415 assigned to the present assignee. These methods provide a digital three-dimensional surface model that is inherently monochromatic, i.e., no color information is obtained in the imaging process.
Associating color information with three-dimensional objects is not straightforward, particularly when the position information is obtained by using a three dimensional scanning method, while the color information is obtained by using a two dimensional scanning method. The problem of conformally mapping the two dimensional color information onto the three dimensional surface model is difficult and it is common for mismatching of the color with three-dimensional points to occur. Essentially, where two-dimensional color detectors are used for obtaining the color information, it is difficult to accurately associate color information from the detectors with the correct points on the three dimensional surface model, particularly where relative movement between the object and the device occurs between the acquisition of the three-dimensional topological data and acquisition of the two-dimensional image data.
EP 837 659 describes a process and device for obtaining a three dimensional image of teeth. Three-dimensional surface data is obtained by first covering the surface with an opaque, diffusely reflecting material, and the object is illuminated with monochromatic light. The image of the object under the layer is obtained by the process described in U.S. Pat. No. 4,575,805 using intensity pattern techniques. In order to obtain a two-dimensional color image of the object, the reflecting layer has to be removed. The method thus requires the camera to be manually re-aligned so that the two-dimensional color image should more or less correspond to the same part of the object as the three dimensional image. Then, the three dimensional image may be viewed on a screen as a two-dimensional image, and it is possible to superimpose on this two-dimensional image the two-dimensional color image of the teeth taken by the camera.
U.S. Pat. No. 6,594,539 provides an intraoral imaging system that produces images of a dental surface, including three dimensional surface images and also two dimensional color images, with the same camera.
In U.S. Pat. No. 5,440,393, the shape and dimensions of a dental patients mouth cavity including upper and lower tooth areas and the jaw structure, are measured by an optical scanner using an external radiation source, whose reflected signals are received externally and converted into electronic signals for analysis by a computer. Both surface radiation and reflection from translucent internal surfaces are scanned, and processing of reflections may involve a triangulation system or holograms.
In U.S. Pat. No. 5,864,640, a scanner is described having a multiple view detector responsive to a broad spectrum of visible light. The detector is operative to develop several images of a three dimensional object to be scanned. The images are taken from several relative angles with respect to the object. The images depict several surface portions of the object to be scanned. A digital processor, coupled to the detector, is responsive to the images and is operative to develop with a computational unit 3-D coordinate positions and related image information of the surface portions of the object, and provides 3-D surface information that is linked to color information without need to conformally map 2-D color data onto 3-D-surface.
Of general background interest, U.S. Pat. No. 4,836,674, U.S. Pat. No. 5,690,486, U.S. Pat. No. 6,525,819, EP 0367647 and U.S. Pat. No. 5,766,006 describe devices for measuring the color of teeth.